Method of detecting protrusion on recording medium and detecting apparatus therefor

Abstract

An acoustic emission sensor is mounted on a flying slider opposed to a rotating recording medium, for example. The acoustic emission sensor outputs a detection signal in response to the sound of collision. When a protrusion exists on the recording medium, the flying slider is expected to collide against the protrusion at a predetermined fixed angular position. A variation is induced in the detection signal based on the collision between the flying slider and the protrusion in synchronization with the rotation of the recording medium. Specifically, when a variation is synchronized with the angular position signal of the recording medium, the variation should correspond to a protrusion existing on the surface of the recording medium. If the component corresponding to the variation is extracted out of the detection signal, a protrusion on the recording medium can be determined at a higher accuracy.

1. A method of detecting a protrusion on a recording medium, comprising:
 obtaining an index signal specifying a standard attitude of the recording medium;  
 generating a sine wave signal based on a period of the index signal, the sine wave signal specifying an angle of rotation of the recording medium from the standard attitude of the recording medium;  
 obtaining a detection signal output from a collision detector designed to detect a collision between a surface of the recording medium and a flying slider; and  
 determining a collision between the surface of the recording medium and the flying slider based on the sine wave signal and the detection signal.  
 
   
   
     2. The method of detecting according to  claim 1 , wherein a constant relative speed is set between the surface of the recording medium and the flying slider during the rotation of the recording medium. 
   
   
     3. The method of detecting according to  claim 2 , wherein said collision detector is designed to detect a sound induced based on a collision between the surface of the recording medium and the flying slider. 
   
   
     4. The method of detecting according to  claim 3 , wherein said collision detector is an acoustic emission sensor mounted on the flying slider. 
   
   
     5. The method of detecting according to  claim 4 , wherein said acoustic emission sensor is a piezoelectric element. 
   
   
     6. The method of detecting according to  claim 1 , further comprising:
 generating a cosine wave signal based on a period of the index signal, the cosine wave signal specifying the angle of rotation of the recording medium from the standard attitude of the recording medium, wherein  
 the collision is determined based on the sine wave signal, the cosine wave signal and the detection signal.  
 
   
   
     7. The method of detecting according to  claim 6 , further comprising:
 generating a first reference signal specifying a product of the sine wave signal and the detection signal;  
 generating a first integral signal specifying an integral value of the first reference signal over a predetermined number of revolution of the recording medium;  
 generating a second reference signal specifying a product of the cosine wave signal and the detection signal;  
 generating a second integral signal specifying an integral value of the second reference signal over a predetermined number of revolution of the recording medium; and  
 generating a comparative reference signal specifying a sum of the integral values of the first and second integral signals, wherein  
 the collision is determined based on the comparative reference signal.  
 
   
   
     8. The method of detecting according to  claim 7 , wherein a constant relative speed is set between the surface of the recording medium and the flying slider during the rotation of the recording medium. 
   
   
     9. The method of detecting according to  claim 8 , wherein said collision detector is designed to detect a sound induced based on a collision between the surface of the recording medium and the flying slider. 
   
   
     10. The method of detecting according to  claim 9 , wherein said collision detector is an acoustic emission sensor mounted on the flying slider. 
   
   
     11. The method of detecting according to  claim 10 , wherein said acoustic emission sensor is a piezoelectric element. 
   
   
     12. A detecting apparatus for a protrusion on a recording medium, comprising:
 a function generating circuit designed to generate a sine wave signal and a cosine wave signal based on rotation of the recording medium;  
 a first multiplying circuit designed to multiply a detection signal from an acoustic emission sensor by the sine wave signal so as to generate a first reference signal, the detection signal designating an elastic wave between a target object and a surface of the recording medium;  
 a first integration circuit designed to calculate an integral value of the first reference signal over a predetermined number of revolution of the recording medium;  
 a second multiplying circuit designed to multiply a detection signal from the acoustic emission sensor by the cosine wave signal so as to generate a second reference signal;  
 a second integration circuit designed to calculate an integral value of the second reference signal over a predetermined number of revolution of the recording medium; and  
 an addition circuit designed to add outputs from the first and second integration circuits to each other.  
 
   
   
     13. The detecting apparatus according to  claim 12 , wherein said acoustic emission sensor is a piezoelectric element. 
   
   
     14. The detecting apparatus according to  claim 13 , wherein said piezoelectric element is a PZT element. 
   
   
     15. The detecting apparatus according to  claim 12 , comprising:
 a spindle motor generating a driving force for the rotation of the recording medium;  
 a flying slider opposed to a surface of the recording medium mounted on a rotation shaft of the spindle motor, said flying slider supporting the acoustic emission sensor; and  
 a controlling circuit designed to control rotation speed of the rotation shaft based on position of the flying slider relative to the rotation shaft of the spindle motor.  
 
   
   
     16. The detecting apparatus according to  claim 15 , wherein said acoustic emission sensor is a piezoelectric element. 
   
   
     17. The detecting apparatus according to  claim 16 , wherein said piezoelectric element is a PZT element.